The invention relates to a method for adjusting the output power for a radio link which uses two different channels, and a corresponding radio station.
In radio communications systems data is transmitted over the air by electromagnetic waves. A mobile radio telecommunication system is an example of a radio communications system. Currently the most widespread standard for mobile radio telecommunication systems is the GSM (global system of mobile communication) standard, which is classed as the second generation of mobile telecommunication systems. The third generation of mobile telecommunication systems is being implemented at the present time. This class includes for example UMTS (universal mobile telecommunications standard) with its two variants TDD (time division duplex) and FDD (frequency division duplex).
The UMTS standard provides for a CDMA (code division multiple access) method of access, in which different links are distinguished from one another by different spreading codes and/or different scrambling codes. One or more channels are allocated to a link. A spreading code and a scrambling code are allocated to each channel. A code known as a primary scrambling code and a plurality of secondary scrambling codes are available. All channels with the same scrambling code are orthogonal to one another. So for example all channels using the primary scrambling code are orthogonal to one another. On the other hand channels using the primary code are not orthogonal to channels using one of the secondary scrambling codes. The simultaneous use of channels with orthogonal codes causes less mutual interference than the use of codes that are not orthogonal to one another. At the same time it is necessary to be aware that although orthogonality may exist transmitter-side, unfavorable transmission conditions (multi-path propagation) can have an adverse effect receiving-side.
When a mobile station is operating a link on a first channel, it is often necessary for said station to run a check on other channels, for example in order to enable a changeover to another channel or to another radio cell. For this reason UMTS provides for mobile stations to be changed over to a mode known as compressed mode, in which data needing to be transmitted to a mobile station is transmitted during a shortened period of time only, so that the mobile station concerned can perform measurements for the remainder of the time. So that the data intended for transmission can be transmitted during this shortened time period, compressed mode briefly uses a spreading code with a spread factor that is smaller than before the changeover to compressed mode and after the end of compressed mode. While so doing it is useful to increase transmission output power in inverse proportion to the reduction in spread factor, in order to ensure approximately the same reception quality.